2010 Toyota Prius Owners Manual - Page 276

2-4. Using other driving systems Disabling pre-collision braking Enabled Disabled The "PCS" warning light comes on when the pre-collision braking is disabled. ITO24P116 Radar sensor Detects vehicles or other obstacles on or near the road ahead and determines whether a collision is imminent based on the position, speed, and heading of the obstacles. ITO24P131 250